Conventionally, as a position detecting sensor, a sensor using a photo interrupter (transmission photo sensor) or a photo reflector (reflection photo sensor) is known.
The photo interrupter is a sensor that has a structure where a light-emitting element for converting an electric signal to an optical signal and a light-receiving element for converting an optical signal to an electric signal are faced to each other with fixed spacing and are integrated into a single housing, and that detects the presence or absence of an object according to changes in quantity of light caused by light passing through the two elements.
On the other hand, the photo reflector is a sensor that has a structure where a light-emitting element for converting an electric signal to an optical signal and a light-receiving element for converting an optical signal to an electric signal are placed on the same side and are integrated into a single housing, and that detects changes in reflected light from an object.
For example, a device described in Patent Document 1 uses a photo interrupter as a position detecting sensor, and has a sensor for detecting the original position of a zoom lens unit or focus lens unit driven in the direction of the optical axis, the sensor being mounted on a lens barrel having a zoom function or focusing function of the digital still camera. The detection of the original position is carried out by using a screening component and a photo interrupter mounted on the lens unit, by driving the lens unit with a motor, by screening light with the screening component when it is moved together with the lens unit and crosses a photosensor, and by monitoring the output level of the photosensor.
Furthermore, a device described in Patent Document 2, for example, employs a photo reflector as a position detecting sensor, has the photo reflector fixed to one of the two relatively rotating components, a fixed collar, for example, and has a reflective component (reflective sheet) fixed with an adhesive to the other component, a rotating collar, for example. Both the photo reflector and reflective component are fixed to predetermined positions so that the origin detection is made at the position where the output of the photo reflector is produced.
Although such devices that employ the photo interrupter or photo reflector as the position detecting sensor are stable in temperature characteristics, they have a problem of increasing size, thereby hindering miniaturization of an AF (autofocus) unit. To solve the problem, a position detecting sensor using a magnet and a magnetic sensor has been developed (see Patent Document 3, for example).
FIG. 1 and FIG. 2 are block diagrams for explaining a conventional position detecting device based on a magnetic sensor: FIG. 1 is a diagram showing a position detecting sensor comprising a magnet and Hall elements; and FIG. 2 is a diagram showing a signal processing circuit of the position detecting device incorporating the position detecting sensor shown in FIG. 1.
As shown in FIG. 1, the position detecting sensor has one magnet (magnetic flux generating body) 1 and two Hall elements (such as a pair of Hall elements (a magnetic sensor pair)) 2a and 2b placed separately from each other. The magnet 1 has a cylindrical shape, whose top side and bottom side are magnetized to the N-pole and the S-pole, respectively. The pair of the Hall elements 2a and 2b are fixed to a fixing side body (fixing component) such as a device body, and the magnet 1 is fixed to a moving side body (moving component) that moves with respect to the fixing component. Then, the magnet 1 fixed to the moving component can move in the direction of the arrow AR1 (X direction) with respect to the Hall element pair 2a and 2b fixed to the fixing component. Here, symbols BD each designate a magnetic flux detection axis.
The signal processing circuit 3 shown in FIG. 2 has differential amplifying sections 11a and 11b, a subtracting section 13 and a low-pass filter 15. The differential amplifying section 11a obtains Hall e.m.f. Vha, the difference between output potentials Va1 and Va2 of the Hall element 2a; and the differential amplifying section 11b obtains Hall e.m.f. Vhb, the difference between output potentials Vb1 and Vb2 of the Hall element 2b. Then, the subtracting section 13 calculates the difference ΔV (=Vha−Vhb) between Vha and Vhb. The output value from the subtracting section 13 passes through the low-pass filter 15, and is output as an output (position output) indicating the position of the magnet 1.
The signal processing circuit 3 further comprises an adding section 14, an arithmetic section 16, and a power control section 17; and these processing sections 14, 16 and 17 control the input voltage Vin to each of the Hall elements 2a and 2b in such a manner that the addition value (sum) of the output voltages (Hall e.m.f.) Vha and Vhb becomes constant. Thus, the signal processing circuit 3 is configured in order that while it controls the input value Vin to the Hall element pair 2a and 2b in such a manner that the addition value (Vha+Vhb) of the output values of the Hall element pair 2a and 2b becomes a constant value Vet, it detects the difference value ΔV between the output values of the Hall element pair 2a and 2b, and outputs as the position output.
However, the foregoing position detecting device incorporating the position detecting sensor including the magnet and the Hall elements has looseness in the moving mechanism (looseness in the vertical direction of the magnet) in general, which presents a problem of causing an error. In contrast with this, the photo interrupter detects the position in the horizontal direction without detecting the looseness in the vertical direction.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a position detecting device and a position detecting method that enable cancellation of variation in the temperature characteristics and elimination of an error due to the looseness in the vertical direction by calculating a ratio between the output voltages of a plurality of Hall elements, and that enable miniaturization.
Patent Document 1: Japanese Patent Laid-Open No. 2006-58818;
Patent Document 2: Japanese Patent Laid-Open No. 2004-132751; and
Patent Document 3: Japanese Patent Laid-Open No. 2005-331399.